A parallel interference cancellation scheme regenerates multi-user signals on a user basis and performs reference cancellation by subtracting regenerated interference signals from received signals, wherein the signals for the multi-users are transmitted in a mixed state.
Since a receiver of a CDMA system receives signals, which are coded by using a unique spread code in each terminal, transmitted through the same frequency band, mixed and, then, received through a channel, its performance is degraded by the multiple access interference (MAI) caused in de-spreading of the received signals.
Further, when subtracting a regenerated baseband signal for each path from a received baseband signal in order to cancel the MAI, the complexity of a system substantially varies according to a location of a band spread filter for converting the regenerated signal to the baseband signal.
A conventional parallel interference cancellation receiver has a drawback that its system complexity is comparatively high since it requires a pulse shaping filter for each finger when regenerating a signal for the interference cancellation. For instance, in case the number of multi-paths (i.e., the number of fingers in each detector) is L and the number of users (i.e., the number of detectors) is K, the number of base spread filters required to perform an S-stage interference cancellation becomes K*L*S.
In case of employing a band spread filter for each detector instead of using a pulse shaping filter for each finger in order to resolve the system complexity, there needs K*S filters and there still remains a complexity problem in case there are a number of users.
In order to solve the above problems, the prior art, ‘CDMA multi-user interference canceller’ (Japanese Patent No. Bei 10-24367) employed only one pulse shaping filter at each interference cancellation node by summing up the regenerated signal of each detector and then allowing the summed signal to pass through the pulse shaping filter.
Since, however, the prior art performs a subtraction process on a chip basis, it does not consider the case that user signals are asynchronous.